The present invention relates to a pulse width controller adopting a feedback pulse width modulation (PWM) integration system employing a carrier-synchronous signal. The pulse width controller employs a pulse signal synchronized with the rising and falling edges of a carrier and, in converting an analog signal into a digital signal, precisely changes the width of an output pulse signal according to the amplitude of an externally applied analog signal.
At present, pulse width modulation is used in various types of equipment. In such equipment, when analog information is to be transmitted, an original analog signal is loaded onto a high frequency carrier and transmitted using a modulation system. The modulation system can be divided into a frequency division modulation subsystem for modulating the amplitude, frequency, and phase of a carrier with respect to an original signal, and a time division modulation subsystem for modulating a carrier by employing a pulse signal.
The modulation techniques used in these subsystems are largely used in communication systems that transmit voice information and images, such as consumer appliances, and are applied to instrumentation control systems such as digital power meters, voltmeters, various recorders, and other industrial instruments. In particular, techniques adopted to analog instrumentation can be extended to analog-to-digital (A/D) conversion. These techniques involve methods for converting analog signals into digital pulse signals and transmitting the results. A pulse amplitude modulation technique and a pulse width modulation technique therefore form the mainstream of precise modulation methods.
Among the precise modulation methods, the PWM integration technique to be applied to an A/D converter can be divided into a voltage-time (V-T) converting system and a voltage-frequency (V-F) converting system, according to the principles of its particular operation.
The V-T converting system generally employs a dual slope integration method and has a relatively simple circuit constitution. However, resolution is limited in this system due to an offset voltage of an integrator, variations in the dielectric characteristics of a capacitor, and the poor resolution and slow response time of a comparator.
To solve these problems, a charge balancing system, i.e., a V-F converting system, has been developed. However, errors still exist in this system due to the high speed of the changes to the input waveform of the comparator, and since the signal applied to the integrator includes a high frequency component.
To reduce these errors, a feedback PWM integration system, i.e., a V-T converting system, that sets a signal converting rate of the comparator to a suitable scope for circuit design and restricts the response of the integrator to a frequency which is somewhat low, has been developed. In this system, however, time is required to integrate the input signal into a correct conversion valued, creating a delay which necessitates a synchronization method in order to improve the response characteristics.
The above discussion primarily deals with methods or means for speeding up the conversion of an integration-type A/D converter, increasing resolution or reducing errors. These methods, however, cannot in themselves offer optimum enhancement for pulse width modulation.